A piezoelectric element (in the present specification, the term “piezoelectric element” encompasses “electrostrictive element”) is an element (device) which contracts or expands upon application of voltage thereto or an element which generates a voltage when it is contracted or expanded. Therefore, such a piezoelectric element is used in various apparatuses; for example, as a drive actuator of an ink injection device of a printer or the like, or as a sensor for measuring viscosity of fluid or the like.
If an anomaly such as generation of a micro crack occurs in such a piezoelectric element, the piezoelectric element cannot provide a desired function. In view of this, in manufacture of piezoelectric elements, inspection is performed so as to determine whether or not an anomaly such as generation of a micro crack has occurred in a manufactured piezoelectric element or to determine whether or not a manufactured piezoelectric element is likely to have such an anomaly later.
Conventionally, such inspection has been performed through, for example, a method of measuring the frequency characteristic of impedance of a manufactured piezoelectric element, and comparing a curve pattern representing the measured impedance frequency characteristic with a curve pattern representing the frequency characteristic of impedance of a piezoelectric element which is normal and serves as a reference for comparison (hereinafter referred to as a “reference piezoelectric element”) (see, for example, Japanese Patent Application Laid-Open (kokai) No. H6-3305).